Various working machines such as a bulldozer and a loader are frequently used at various working sites such as construction sites and civil engineering sites. A blade, which is a work implement, is attached to the working machine of this kind. The blade is widely used for excavation, soil transportation, earth filling, piling and dozer working.
In order to exhibit the maximum operation efficiency in the working machine, it is important to increase the amount of soil to be transported as much as possible, to reduce the resistance in excavation and soil transportation as low as possible, and to adapt to different kinds of soil. If earth filling, soil piling and ground making can be carried out at the same time, this is preferable because the operation efficiency is remarkably improved. If optimal structure, shape, width and height of the blade, a position and excavation angle of a cutter (cutting edge) which satisfy these conditions are found, there are merits that the operation efficiency of the working machine is improved, fuel consumption amount is reduced, and the entire operation period can be shortened.
As one example of the blade device for increasing the operation amount of the working machine of this kind, the present applicant previously proposed Japanese Patent No. 2757135 (patent document 1). The patent document 1 discloses the blade device which can control the position of the blade attached to a front portion of a large-scale bulldozer in each of the excavation step, the soil transportation step and the soil discharging step. According to the blade device disclosed in this patent publication, a blade drive hydraulic device is controlled such that the blade is inclined backward (pitch back) with respect to the position at the time of excavation through a predetermined angle when soil is transported, and the blade is inclined forward (pitch dump) with respect to the position at the time of excavation through a predetermined angle when soil is discharged.
In order to exhibit the work capability of the bulldozer at a maximum, the balance of force in the soil transportation operation of the bulldozer is controlled such that the traction force is larger than soil transportation resistance and a driving force of the vehicle is larger than the traction force as described in the patent document 1. In the patent document 1, the traction force can be increased and the soil transportation resistance can be reduced by controlling the position of the blade as described above, and in order to increase the operation amount of the bulldozer, it is possible to largely increase the soil transportation amount without increasing the bulldozer in size, without increasing the engine output or without increasing the blade in capacity.
In the bulldozer, most of engine output required when the excavation and soil transportation operations are carried out is consumed by the driving force of the vehicle and the traction force at the time of the excavation and soil transportation. Therefore, it is important to reduce the loss in energy amount during power transmission and to improve the fuel efficiency. Further, it is strongly required to reduce the resistance during the excavation and soil transportation operations. Generally, in the case of a middle scale or a small scale bulldozer, a distance of soil transportation is shorter as compared with a large scale bulldozer. If the above-described requirements are satisfied, it is possible to effectively use the engine output during the excavation and soil transportation even with a traction force and a blade having the same volume as that of the conventional device.
Conventionally, in view of such circumstances, there is proposed a blade structure in which a first blade member is mounted on a lower end front portion of a machine body of an earthmoving vehicle, and second blade members are bent forward from both left and right ends of the first blade member as disclosed in Japanese Utility Mode Application Laid-open No. 4-92064 (patent document 2). The blade disclosed in the patent document 2 is called U-dozer and is used, a blade face is formed into various shapes such as an arc face having a constant curvature and a curved face having vertically different curvatures, but it is not concretely described that the horsepower consumption per a traction force in the excavation and soil transportation operations can be reduced and the fuel efficiency can be improved. There is no conventional technique which can effectively use the energy amount during the excavation and soil transportation and which can reduce the fuel consumption at the same time.
Hence, to solve such problems, the present applicant proposed a quite new blade structure in International Patent Application Laid-open No. 2004/044337 (patent document 3). The blade disclosed in the patent document 3 includes a central front face, coupling front faces extending from left and right ends of the central front face extending such that the coupling front faces are bent backward and spreading, and end front faces extending from the coupling front faces such that the end front faces are bent and spreading forward. A lower end of the central front face has a predetermined blade width extending laterally intersecting orthogonally with the excavation direction, the lower end has a first cutter, the coupling front faces and the end front faces are provided at their lower ends with second and third cutters. Cross lines of the coupling front faces and the end front faces and intersection between the tips of the second cutter and the third cutter are located at retracted position retracted from the tip of the first cutter as viewed from above. The central front face, the coupling front faces and the end front faces are respectively formed into concave curved faces which extend continuously from upper ends to lower ends thereof, and the central front face has such a special shape that its lower end has a small blade width and the blade width is gradually increased toward the upper end.
A working machine to which the blade of the patent document 3 is applied includes construction or earthmoving machinery, and representative examples thereof are construction or earthmoving vehicles such as a bulldozer, a wheel dozer and a motor grader. Expressions “as viewed from front” and “as viewed from above” of the blade device according to the present invention used in this specification means “as viewed from front” and “as viewed from above” when the blade comes into contact with the ground at a tip angle having high excavation efficiency, and “front” and “rear” means “front” on the side of a ground-contact face of the blade device and the other side is called rear. Further, “lateral direction” of the blade device is a direction intersecting orthogonally with the longitudinal direction as viewed from above.
The blade of the blade device includes a central front face constituting a portion of a blade front face, and left and right end front faces projecting from the left and right ends of the blade such as to spread forward as in the conventional semi-U type blade, but the blade of the present invention is largely different from the conventional blade in that coupling front faces are disposed between the central front face and the left and right end front faces, the left and right coupling front faces extend such as to bend at the left and right ends of the central front face such that the coupling front faces spread rearward, and the left and right end front faces extend from the rear end edges of the coupling front faces such that the end front faces spread in parallel to the extension of the lower end of the central front face or forward.
A blade which is different from that applied to various operations such as excavation, soil transportation and ground making but which has similar shape as that of the present invention is disclosed in International Patent Application Laid-open No. 93/22512 (patent document 4). The blade described in the patent document 4 is applied to a reclaiming compression working vehicle which compresses garbage while spreading the same at a waste dump. Like the conventional blade, this blade shape includes end blade portions projecting from left and right ends such as to spread in a form of wings in the running direction of the vehicle, one flat-plate like central blade portion connecting the left and right end blade portions with each other, and a rectangular box like projection which inclines downward from an intermediate portion of the central blade portion in the vertical direction such as to project in the running direction of the vehicle. Steel wheels are employed for a running device of the compression working vehicle, and garbage is compressed and processed by the wheels. The blade disclosed in the patent document 4 is developed with the emphasis on a function for dispersing garbage, and on a function in which a processing amount for compressing the garbage is controlled, and an amount of garbage to be sent to a space formed between left and right wheels which are the compressing members is limited so that a case where an excessively large amount of garbage enter the space and a lower face of the vehicle is damage is avoided. Therefore, the shape and functions of the blade of the patent document 4 are largely different from those of the blade of the patent document 3 having originally different function.
That is, (1) the central front face of the blade described in the patent document 3 deposits and holds a large amount of excavated earth and sand and thus, the central portion of the blade is continuous from the upper end to the lower end, but the central projecting portion of the blade in the patent document 4 corresponding to the central front face projects toward the lower end from the intermediate portion between the upper end lower ends of the central blade portion because a main purpose thereof is to eliminate excessive garbage, and (2) the intersection between the pair of left and right coupling front faces and the end front faces in the patent document 3 is located behind the central front face as viewed from above, and the tip ends of the end front faces extend to a location near the extension of the lower end edge of the central front face, but in the patent document 4, tip ends of the pair of left and right end blades projecting forward from the central blade portion are located in front of the projecting lower end edge of the central projection in any of the drawings although it is not described in sentences of the patent document 4. These differences are from the originally different functions of the blades disclosed in the patent documents 3 and 4 as described above.
Patent document 1: Japanese Patent Publication No. 2757135
Patent document 2: Japanese Utility Mode Laid-open Publication No. 4-92064
Patent document 3: International Patent Laid-open Publication No. 2004/044337
Patent document 4: International Patent Laid-open Publication No. 93/22512